In the field of FA (Factory Automation), a variety of image processing techniques are used. Typically, an image processing technique of recognizing characters printed on a test object or inspecting a test object for defects and the like on its surface based on image data obtained by capturing an image of the test object is widely used in practice.
When a variety of measurement processing is performed on a test object using such an image processing technique, it is necessary to acquire an image representing the test object appropriately. Therefore, an illumination apparatus for illuminating a test object is often provided to ensure an appropriate illuminance during image capture. Illumination apparatuses using long-life and low-power-consumption LEDs (Light Emitting Diode) are in practical use.
For example, a ring-shaped illumination apparatus disclosed in Japanese Patent Laying-Open No. 2008-139708 (PTL 1) is configured to include a plurality of concentrically arranged LED rows and a plurality of optical members concentrically arranged to correspond to the LED rows. The manner in which the LED row illuminate a work is different from one another. The optical members are continuous to form an integral structure. Accordingly, a single apparatus can be adapted for different kinds of object lens and work.
An LED illumination apparatus disclosed in Japanese Patent Laying-Open No. 2009-146841 (PTL 2) is structured such that a positioning pin provided on a flat base is inserted into a through hole provided on a flat LED substrate having a plurality of LEDs thereon and into a positioning pin insertion hole provided on an integral lens holder for holding a plurality of lenses, whereby the lens holder is positioned with respect to the LED substrate. Accordingly, individual lenses can be positioned with respect to a plurality of LEDs.